The field of the invention relates to internal combustion engines having vacuum assisted brake systems.
Internal combustion engines are known that improve thermal efficiency and reduce pumping work by operating lean of stoichiometry and increasing manifold pressure. It is also known to extend lean operation by performing stratified operation where fuel is injected directly into the engine cylinder during a compression stroke. These engines also are capable of performing homogeneous operation where fuel is injected during an intake, or suction, stroke. Typically, stratified operation is limited to lean air/fuel ratios, while homogeneous operation can be both lean and rich of stoichiometry.
Vehicle brake systems are also known that use vacuum assist to increase driver braking force. In these systems, vacuum generated by engine operation provides extra force to assist driver braking. When these braking systems are combined with lean burn engines, engine operation may be controlled so that desired vacuum is supplied during braking. One approach uses a vacuum pressure sensor located in a brake booster to indicate available braking vacuum. When available vacuum falls below a predetermined value, engine air/fuel ratio is decreased toward stoichiometry and stratified operation is discontinued. Such a system is described in U.S. Pat. No. 5,826,559.
The inventors herein have recognized a disadvantage with the above approach. In particular, vehicle cost is increased since an additional sensor is added to determine vacuum level.
An object of the present invention is to determine brake booster vacuum without, or in addition to, a brake booster vacuum sensor.
The above object is achieved and disadvantages of prior approaches overcome by a method for determining pressure in a brake booster coupled through a check valve to a manifold of an internal combustion engine, the method comprising: measuring an operating parameter; and calculating an estimate of the brake booster pressure based on said operating parameter.
By estimating brake booster pressure from other known operating conditions, it is possible to provide engine control systems with the information necessary to maximize fuel economy and minimize emissions, without adding additional sensors. In other words, by exploiting knowledge of physical relationships between systems, it is possible to estimate necessary brake booster parameters without use of an additional sensor.
An advantage of the above aspect of the present invention is that improved fuel economy and reduced emissions can be achieved without additional cost.
Another advantage of the above aspect of the present invention is that if a brake booster sensor is presently used, the sensed value can be complemented with an estimated value to improve accuracy.
In another aspect of the present invention, the above object is achieved and disadvantages of prior approaches overcome by a method for determining pressure in a brake booster coupled through a check valve to a manifold of an internal combustion engine, the brake booster coupled to a driver actuated hydraulic brake system, the method comprising: measuring an engine operating parameter; measuring a brake system parameter; and calculating an estimate of the brake booster pressure based on said engine operating parameter and said brake system parameter.
By using both engine operating parameters and braking system parameters, it is possible to estimate brake booster pressure continuously during vehicle operation. In particular, engine operating parameters mostly indicate how brake booster pressure can decrease, while braking system parameters mostly indicate how brake booster pressure can increase. In this way, brake booster pressure can be estimated and used to improve other engine operations.
An advantage of the above aspect of the present invention is that improved fuel economy and reduced emissions can be achieved throughout vehicle operation without additional cost.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.